Experimental Study on Surface Integrity of Single-Crystal Nickel-Based Superalloy Under Various Machining Processes

Abstract

AbstractNickel-based superalloys have the ability to retain superior mechanical and chemical properties at elevated temperatures. Therefore, these alloys become an ideal material choice for use in the hot sections of gas turbine engines. Advanced cast, single-crystal castings offer higher creep strength and thermal fatigue resistance than the columnar grained and polycrystalline castings. The castings undergo certain precision machining operations to obtain required fitment geometries during the engine assemblies. However, the nickel-based superalloys are considered as difficult-to-cut materials. High cutting forces and heat are generated while machining these alloys, which results in premature failure of cutting tools and poor integrity of the machined surfaces. The surface integrity aspects are of prime concern in the aerospace applications. This paper presents the results of the vital surface integrity aspects (i.e., surface topography and surface metallurgy) of a 2nd-generation single-crystal nickel-based superalloy under various precision machining process, namely milling, grinding WEDM and AWJM, which induces certain thermo-mechanical loads. It is observed that the ground surface has a highest surface finish (0.2 µm Ra) by the cutting and polishing action of multiple cutting points under higher cutting velocity. WEDM surface has lowest machining effect zone (10 µm) though it has highest surface roughness, misorientation angle, and degree of work hardening on the machined surface. Recrystallization and surface cracks were not observed at the machined surfaces under the subjected machining conditions.KeywordsSingle-crystal nickel-based superalloyMachining processSurface integritySurface topographySurface metallurgy